1. Field of the Invention
This invention relates to methods and indicators of authenticity. The system of the invention is useful in the authentication of security papers. The invention is particularly useful with documents, tags and labels.
2. Description of Related Art
Indicators to ascertain the genuineness of documents, tags and labels have been proposed in several different forms.
U.S. Pat. No. 3,063,163 to Carmeli teaches a method of detecting counterfeit currency substrates by applying an iodine solution to the substrate to react with starch yielding a brown to black marking. Carmeli is a negative indicator in that genuine currency does not undergo a color change. Counterfeit currency on the other hand forms a bluish black mark with the iodine indicator, attributed to a difference in starch content. The marking is fairly permanent, however can be made to dissipate over a few days by inclusion of oxidizing agent.
Wood U.S. Pat. No. 4,037,007 teaches secure documents with color forming planchettes. A color forming reaction of azo compounds or lactone or leuco compounds with an organic acid is taught for forming a color change or change from colorless to colored form.
Collings, U.S. Pat. No. 5,188,887 teaches an authentication system comprising a paper carrying a starch and iodate salt to which an authenticating solution of an iodide salt is applied. Collings U.S. Pat. No. 5,261,954 teaches combinations of iodide salts together with a variety weak acids applied to starch and iodate bearing papers. These patents teach presence of iodine salts in both the paper substrate and applicator.
Use of iodide and iodate in security papers can be traced to patents such as Carvalio U.S. Pat. No. 531,507 which taught blending paper pulp with a combination of bismuth iodide and sodium iodide; and Menzies U.S. Pat. No. 302,758 taught paper coated or immersed into a solution of potassium iodide and iodate. Papers laced with such materials are described as useful for detection of forgery or attempted alteration.
Carmeli U.S. Pat. No. 5,063,163 is a more recent example of a method to detect authentic currency taking advantage of the starch content by applying an iodine solution to the currency paper.
More recently Ukpabi U.S. Pat. No. 7,163,909 taught a rapidly reversing indicator based on application of selected acidic solutions to a paper coated with phthalide, leucauramine or fluoran chromogens.
Although the various above described systems have utility for certain applications, a need exists for more selective authenticity indicators. Many of the above systems are commonly used giving rise in some applications to increased likelihood of false positives, such as when an iodine indicator is applied to a starch coated paper, even though not currency. Where applicators are used, it is also desirable to minimize use of stain-producing materials to reduce messiness in use, or to avoid use of ingredients perceived as environmentally less desirable or undesirable from a safe handling or neatness aspect.
These and other aspects such as the desire for systems unique to a manufacturer have given rise to a need and desire for improved authenticity indicators.